Recently, an electronic endoscope wherein such solid state imaging device as a charge coupled device (CCD) is used as an imaging means is variously suggested.
Such electronic endoscope has advantages as compared with a fiber scope that the resolution is higher, it is easier to record and reproduce picture images and such picture image processing as the magnification and comparison of picture images is easier.
Now, in the case of observing an object by using such imaging apparatus as the above mentioned electronic endoscope, particularly, in the case of distinguishing the affected part and normal part from each other within a living body, it will be necessary to sense (recognize) a delicate tone difference. However, in case the variation of the tone in the observed part is delicate, a high knowledge and experience will be required to sense .this delicate difference. Further, a long time will be required until it is sensed. Even if attentions are concentrated during the sensing, it has been difficult to always make a proper judgment.
In order to cope with such circumstances, for example, in the publication of a Japanese patent application laid open No. 3033/1981, by noting that, in such other range than the visible range as, for example, an infrared wavelength range, some variation of the tone may be large, there is disclosed a technique wherein a spectral light having at least one infrared wavelength range is led in time series to illuminate an object to be observed, the reflected light from the observed object is made to form an image on a solid state imaging device and is converted to a electric signal and the electric signal is processed in response to the wavelength range to display a picture image in the wavelength range with a specific color signal. According to this prior art example, the invisible information obtained in the infrared wavelength range can be converted to a visible information and, for example, the affected part and normal part can be quickly and easily discriminated from each other.
On the other hand, it is known to be useful for the early discovery or the like of a disease to know the amount of hemoglobin and the distribution of the oxygen saturation degree in a blood. As a method of determining the amount of hemoglobin and the oxygen saturation degree in the blood, for example, as shown in the publication of a Japanese utility model application laid open No. 151705/1986, there is a method of determining them from picture images in a plurality of specific wavelength ranges.
However, in the above mentioned prior art example, the combination of illuminating lights, that is, the observing wavelength is fixed (by the combination, for example, of green, blue and infrared if they are used) and the combination of illuminating lights could not be simply varied. That is to say, in the case of observing by varying the combination of illuminating lights, the rotary filter will have to be replaced each time. Further, the combination of green, blue and infrared will not be always effective to all the disease parts. That is to say, it is well considered that, in some affected part, as compared with the stomach wall, the absorption coefficient in the wavelength range on the side of the wavelength longer than of the red light or in the short wavelength range is greatly different.
The medical study of the special light observation has not yet been well made but will be positively made hereafter. It is strongly required that the disease part should be observed by varying the combination of illuminating lights and what combination of illuminating lights is effective to the discrimination from the peripheral side part depending on the kind of the disease part should be investigated and should be applied to the diagnosis on the basis of the results.